e-mail attachments-videos

I'm running Vista, and I've recently ran into a problem. I've always
normally been able to open up my attachments that are videos by the usual
double click, a futher window pops up to Open, indicating that it'll open up
using Windows Media Player, I clicked on Open and it would begin. Now when
I do the aforementioned and the window comes up and I click on open, it
begins playing, however to view it I have to click on the icon Windows Media
Player before the actual e-mail will disappear and the video is able to be
viewed. Why would this have just occurred, has it something maybe due to
their recent updates etc.
Any assistance gladly welcomed.
tks Rick